Sommaire partiel One of the main hypotheses of this thesis was that biochar can reduce pathogens from water
in a filter system and later be used as fertilizer because of its large surface area and reactivity.
It was concluded that waste water treatments with a biochar filter is possible. The mean path
ogen reduction in the filter was 1.8 log units for E.Coli and enterococci but a loading of bio
char with nutrients was not found. Especially Mg, K and P contents of biochar were reduced.
However, when the treated water is used for irrigation the loss of nutrients from biochar into
the water is not problematic. Despite the lower nutrient content of the filterchar, the crop
yields were still significantly higher than the control treatments and not statistically different
from the yields obtained when untreated biochar was used. The analysis of plant tissue
showed that a direct P fertilizing effect of biochar was mainly responsible for the increases in
crop yields. Other authors reported the loading of biochar with diary effluent or effluent from
an anaerobic digester (Ghezzehei et al. 2014, Sarkhot et al. 2012, Streubel et al. 2012). It
seems that the ability to recover nutrients with biochar from water is controlled by the nature
and properties of the waste stream (form of nutrients) and the properties of biochar (sorption
properties, surface area, etc.). Especially the properties of biochar can be very specific de
pending mainly on feedstock for pyrolysis, the production method, degree of oxygen exclu
sion and pyrolysis temperature (Enders et al. 2012, Rajkovich et al. 2011, Steiner 2016). Es
pecially the rice husk biochar used in this study was produced at KNUST in Kumasi, Ghana.
The custom made pyrolysis reactor allows only little monitoring and produces a very ash rich
biochar (Atijah 2017). In addition, rice husk is a very unique feed stock because of its rela
tively low carbon and high silica content (Yalçin und Sevinç 2001). Also in the lysimeter study, the rice husk biochar was not able to reduce nutrient leaching and
has a low surface area compared to other biochars (Atijah 2017). This may explain why this
biochar was not loaded with nutrients. Nevertheless, the hypothesis that biochar can be used
in waste water filtration holds true. Although, biochar was not enriched with nutrients it still
showed a significant beneficial effect on crop yields.